As a result of the intermittent combustion of modern internal combustion engines, exhaust gases may be discharged after combustion from the at least one cylinder in the context of a gas exchange and to supply charging air or a fresh admixture again. In principle, two-stroke methods and four-stroke methods may be distinguished from each other. First, the gas exchange of the four-stroke method is discussed in greater detail below.
In the four-stroke method, the discharge of the combustion gases is brought about in the context of the gas exchange via the outlet openings and the cylinder is filled with a fresh admixture or charging air via the inlet openings. The outlet openings and the inlet openings, may both also be referred to as simply openings.
In four-stroke engines, globe valves are used almost exclusively to control the gas exchange and carry out an oscillating travel movement during the operation of the internal combustion engine, and thereby open and close the inlet and outlet openings, respectively.
The valve actuation mechanism required for the movement of the valves, including the valves themselves, is referred to as a valve train. The function of the valve train is to open or close the inlet and outlet openings of the cylinders at the correct time, with it being desirable to have rapid opening of flow cross sections which are as large as possible in order to keep the throttle losses low in the incoming and outgoing gas flows and to ensure that the cylinders are filled with a fresh admixture as well as possible and to ensure effective discharge of the combustion gases. The cylinders may also be provided with two or more inlet and outlet openings. The internal combustion engine to which the present disclosure relates may also be operated with the four-stroke method, where applicable, for which reason the at least one cylinder has at least one outlet opening and at least one inlet opening.
The globe valves which may be moved, that is to say, displaced, along their longitudinal axis between a valve closure position and a valve opening position in order to release or block an opening of a cylinder. On the one hand, resilient valve devices are provided to actuate a valve, in order to pre-tension the valve in the direction of the valve closure position and, on the other hand, a valve actuation device is used in order to open the valve counter to the pre-tensioning force of the resilient valve device.
The valve actuation device comprises at least one camshaft, on which a plurality of cams, in this instance at least two cams, are arranged and which is caused to rotate by the camshaft—for example, by a chain drive—in the four-stroke method in such a manner that the camshaft rotates with the cams at half the speed of the camshaft. An operating cycle extends over two camshaft rotations and comprises four operating phases, that is to say, the compression and expansion as a result of the combustion of the fuel/air admixture in addition to the intake and discharge.
In principle, a distinction is made between a lower camshaft and an upper camshaft, reference being made to the plane of separation between the cylinder head and the cylinder block.
Bottom-mounted camshafts are suitable for actuating so-called side-by-side valves but also using push rods and levers, for example, pivot levers or tilting levers, for actuating overhead valves. Side-by-side valves are opened by being displaced upwards whereas overhead valves are opened by a downward movement. A tappet is generally used as an intermediate element and is intended to be engaged with the cam of the camshaft at least during the opening and closing operation.
However, overhead camshafts are used exclusively for actuating overhead valves, a valve train having an overhead camshaft having as an additional valve train component a pivot lever, a tilting lever or a tappet. The pivot lever rotates about a fixed rotation location and, in the event of deflection by the cam, displaces the valve counter to the pre-tensioning force of the resilient valve device in the direction of the open valve position. In the case of a tilting lever which may be pivoted about a centrally arranged center of rotation, the cam engages at one end of the tilting lever, the valve being arranged at the opposite end of the lever. It is advantageous when overhead camshafts are used that the moved mass of the valve train is reduced in particular by dispensing with the push rod and the valve train is more rigid, that is to say, less resilient. At least two bearings which are arranged generally in or on the cylinder head in the case of overhead camshafts are intended to be provided to receive and support the camshaft. If a tappet is used as a cam follower, the tappet is positioned on the end of the globe valve remote from the combustion chamber so that the tappet participates in the oscillating travel movement of the valve when the cam is in engagement with the tappet in the region of the cam lug and deflects it.
In the context of the present disclosure, intermediate elements of the valve actuation device, that is to say, valve train components which are located, that is to say, arranged, in the force path between the cam and the valve are referred to as cam followers, that is to say, they are combined using that term.
In contrast to the above-described four-stroke method, the gas exchange in the two-stroke method is not carried out by discharge and intake by an oscillating piston but instead by the combustion chamber being purged with charging air or a fresh admixture using a pressure drop generated over the combustion chamber, the so-called purging pressure drop.
In a two-stroke engine, slots may be provided for the gas exchange in the cylinder, that is to say, in the cylinder pipe. These slots may be controlled by an oscillating piston, that is to say, they are opened in order to supply charging air and/or to discharge the exhaust gases and are closed for compression and expansion. An operating cycle extends over a camshaft rotation and comprises two operating phases, compression and expansion, following the combustion of the fuel/air admixture. The operating phases intake and discharge are dispensed with or are replaced by a purging operation.
The two-stroke method has several advantages in relation to the four-stroke method, some of which may be attributed to the fact that the operating cycle according to the two-stroke method extends over one crankshaft rotation whereas it extends over two crankshaft rotations in the case of the four-stroke method. In principle, the two-stroke method is characterized by a lower friction action. Furthermore, the engine speed may be reduced, for example, the idling speed may be halved. As a result of the doubled number of operating cycles for the same crankshaft speed, it is further possible to perceptibly increase the maximum torque or—provided that the torque supply remains the same—to reduce the mean pressure. Advantages result in conjunction with the acoustics of the internal combustion engine, which contributes substantially to the overall noise emission of the motor vehicle. By the mean pressure being reduced, the combustion temperatures may be reduced, whereby it is possible to counteract the formation of nitrogen oxides and/or soot. Owing to the smaller mechanical and thermal loads, the internal combustion engine could be constructed in a more filigreed manner with materials being saved, whereby in particular the weight but also costs are reduced.
In comparison with the four-stroke method, however, the two-stroke method also has disadvantages which may mainly be attributed to the poorer, that is to say, not very effective, gas exchange, that is to say, the purging. Owing to the purging, the two-stroke method results in substantially higher emissions of unburnt hydrocarbons and carbon monoxide, the purging of the combustion chamber with charging air or a fresh admixture becoming increasingly poor, that is to say, more inefficient, with increasing speed ηmot, for which reason two-stroke methods are less suitable for high speeds in principle.
In order to be able to use the advantages of the two-stroke method, internal combustion engines which may be operated both by two-stroke methods and by four-stroke methods are being developed. In order to change the internal combustion engine from the two-stroke method to the four-stroke method, that is to say, to switch to the four-stroke method, various concepts have been developed.
The translation of European patent specification DE 601 17 553 T2 describes a selectable camshaft drive for an internal combustion engine which may be selectively operated using the two-stroke method or four-stroke method. The at least one camshaft is permanently in engagement with a planet gear mechanism which is driven by the camshaft. The camshaft is driven either in accordance with the two-stroke method at the camshaft speed or in accordance with the four-stroke method at half the camshaft speed, the gas exchange being carried out via the inlet openings and the outlet openings of the cylinders which are controlled in both operating modes using the at least one camshaft by cams.
Against the background of the above, an objective of the present disclosure is to provide an internal combustion engine may be readily changed from the two-stroke method to the four-stroke method—and vice versa. In the internal combustion engine according to the present disclosure, the at least one camshaft of the valve actuation device for actuating at least one valve has different cams which are used, that is to say, are active, in accordance with the current operating method, respectively.
Since the internal combustion engine in this instance may also have a single cylinder having a single outlet opening and the gas exchange according to the two-stroke method does not have to make use of the at least one inlet opening of the cylinder in each case, but may also be carried out via inlet slots, the camshaft has according to the disclosure a pair of different cams for at least one valve, that is to say, in this instance for the at least one outlet valve of the at least one cylinder.
Such a valve which may selectively be actuated by a first cam or by a second cam in order to be controlled and actuated in accordance with the two-stroke method or in accordance with the four-stroke method, is referred to as a mode-adaptable valve in the context of the present disclosure because the valve actuation or the valve actuation device is adapted to the operating mode, that is to say, the cam used is selected in accordance with the operating mode selected.
In some embodiments both the inlet valves and the outlet valves may be constructed as mode-adaptable valves, the actuation of the inlet valves and the outlet valves being able to be carried out via a common camshaft or via separate camshafts, that is to say, at the input side via an input camshaft and at the output side via an output camshaft. Logically, the valve actuation device of the internal combustion engine according to the disclosure may comprise at least one camshaft having a plurality of cams in order to actuate the valves.
In order to be able to change, that is to say, switch, the cam for actuation in the case of a mode-adaptable valve, the valve train may be constructed so as to be switchable, according to the disclosure in such a manner that the actuation of the valve is carried out in the four-stroke mode by the second cam and in the two-stroke mode by the first cam. In the context of the description of the advantageous embodiments, examples of a valve train which may be switched in that manner are set out.
According to the disclosure, there is arranged in the intake system of the internal combustion engine a mechanical charger, with which a positive pressure drop may be generated over the combustion chamber at any time and operating point of the internal combustion engine, in order to be able to carry out an effective purging operation according to the two-stroke method.
Systems and methods are provided for operating an internal combustion engine in a two-stroke mode or a four-stroke mode to achieve greater fuel efficiency and minimize emissions. The system comprises a mode-adaptable valve; a valve rocker arm to actuate opening and closing of the mode adaptable valve; a cam follower of a first cam for carrying out a two-stroke mode; a cam follower of a second cam for carrying out a four-stroke mode; and a pin to mechanically couple the valve rocker arm to the cam follower of the first cam or the cam follower of the second cam. Coupling the valve rocker arm to the cam follower of the first cam enables a two-stroke mode and coupling the valve rocker arm to the cam follower of the second cam enables a four-stroke mode.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. Further, the inventors herein have recognized the disadvantages noted herein, and do not admit them as known.